The present invention generally relates to an apparatus for characterizing an optic and, in particular, relates to one such apparatus wherein a light beam is directed toward an optic at an angle that ensures total internal reflection of the light within the optic.
There are many techniques for characterizing optical elements. For example, many optics can be readily characterized by the use of interferograms. Such interferometric techniques are well known in the field of optics and a detailed discussion is not believed necessary herein. As is well known, however, interferograms generally provide useful information only about the surface of the optic being examined. Hence, such techniques are not beneficial when the optic being characterized is a window. Further, because of the complexity of the equipment involved, interferometry is not a technique readily adaptable for characterizing an optic once that optic has been installed and is in use.
Currently, in the case of characterizing an optical window, particularly characterizing such a window in-situ, an instrument that directs a light beam of a single visible wavelength is available. Such an instrument measures the direct scattered light from the surface of the optic being characterized. One such instrument is portable and hence can be used to characterize optics both before and after the optic is installed and used.
However, such an instrument has a number of significant drawbacks. The primary drawback is that only the surface of the optic is characterized. The current instruments do not provide information about the internal integrity of the optic. In addition, the single wavelength limitation of such instruments limits the usefulness of such instruments since the particular wavelength available may not be indicative of the performance of the optic being characterized. This is particularly true in cases where the optic being characterized has different coatings on the surfaces thereof. Further, such instruments usually only characterize a relatively small area of the surface of the optic. This limitation is a result of the relatively small spot sized provided by the available instruments. Hence, in order to characterize an entire optical surface, the spot would have to be moved over each point of the surface. Such an analysis would be quite time consuming.
Consequently, there is a considerable need for an apparatus for characterizing an optic that overcomes the above-recited drawbacks of conventional apparatus.